The invention relates generally to solar panels and, more particularly, to a generic solar array panel which utilizes a printed circuit substrate.
A conventional solar array panel has a multiplicity of solar cells mechanically mounted to an aluminum honeycomb panel, or other substrate, and electrically connected to each other using small metallic interconnectors to result in a solar power supply network. The solar cells and their accompanying circuitry transform sunlight into electrical energy, the voltage of which is controlled by the number of solar cells connected in electrical series. Maximum solar power output for a panel of a given size is achieved by maximizing the packing density of the solar cells on the exposed area of the substrate.
The manner in which the solar cells are physically and electrically arranged is normally custom designed for each application and depends on such factors as the substrate dimensions, the electrical requirements of the completed solar array, and the requirements for other electronic components such as protective blocking and shunting diodes necessary to prevent major or total array failure in the event of an electrical short developing in a solar cell string, failure of a solar cell, or shadowing of a portion of the solar array. Constructing such solar array panels while maximizing power output and minimizing panel size, weight, and cost presents several difficulties to which this invention is addressed.
A main difficulty involves making and maintaining the large number of electrical connections required between the individual solar cells as well as between the solar cells and other electronic components in the network. Conventionally, these connections are made with small metallic, often foil, tabs which must be soldered on individually and which may be quite fragile. This results in a solar array panel with a costly, labor-intensive construction process as well as with less than optimal reliability.
Also, conventional solar cells often have their positive and negative terminals on opposite sides of the cell. Therefore, a shingle-like assembly for series interconnection of the positive terminal of one cell to the negative terminal of the next is often employed. This shingled arrangement, in combination with the delicate metallic interconnectors, causes complications in the rework or replacement of one or more broken or dysfunctional cells on a panel. Moreover, this type of assembly is inefficient as portions of each cell are covered by an adjacent cell and results a needlessly high number of solar cells and in unnecessary panel weight.
Present solar panel designs further require hard wiring to conduct the collected electrical power to the load. Electrical harnesses are often routed and bonded to the back side of the substrate, necessitating feed-through holes from the solar cells on the front to the back side. Routing and bonding these wires likewise can be labor intensive and lead to complicated rework and repair.
It is, therefore, an object of the present invention to provide a relatively low cost and reliable solar panel that is simple to construct and repair. It is also an object to provide means for maximizing the packing density of the solar cells on the panel in order to maximize power output while minimizing panel size and weight. This is especially important for solar panels used in satellite and spacecraft applications wherein optimum utilization of available solar array substrate area is essential.
Finally, it is an object of the present invention to provide a generically designed substrate and circuit means, adaptable to virtually any customized panel design for given power requirements.
The foregoing and other objects of the present invention have been attained by providing a generic printed circuit substrate onto which the solar cells and other electronic components are mounted. Formed on the substrate, or encapsulated therein, are all of the cell to cell interconnections as well as connections between the cells and other circuit elements. An integral bus line, also encapsulated within or formed on the substrate, eliminates the need to hardwire the collected power to the load.
Electrically conductive interconnect pads are provided on the substrate top, or exposed, surface for physically mounting the solar cells onto the substrate as well as facilitating their electrical series interconnection, thereby eliminating shingle-like assembly and simplifying rework and repair or broken or dysfunctional cells. Electrically conductive mounting pads for blocking and shunt diodes are provided on the back side of the substrate so that these components can be easily mechanically and electrically connected to the solar array panel. This enables maximum packing densities of the solar cells on the panel as the entire top surface of the solar panel is available for solar cell layout.
The interconnect substrate circuitry is generally designed such that a multiplicity of solar cells are connected in electrical series. Design options of ending a series string at any given location are provided by enabling the series connection between two adjacent cell locations to be interrupted by punching out a small area of the substrate at that location. Cross hatches or other marks can be printed on either of the substrate surfaces to indicate the area of the substrate to be punched out.
Another feature of the preferred embodiment of this invention provides the ability to reliably mount, by soldering or other like process, the silicon solar cells to a printed circuit substrate. This is accomplished by routing stress relief loops into the circuit substrate. The stress relief loops allow the interconnect pads onto which the solar cells are mounted to move relative to the rest of the substrate. This relieves the stress to the solder joint created by differences in the characteristics of thermal expansion between the solar cell and the printed circuit substrate.
Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.